The present invention relates to a process for the catalytic hydrovisbreaking of a hydrocarbon charge in the presence of a catalytic composition comprising at least one metal selected among the metals from groups VI B, VII B and VIII of the periodic table of elements (Handbook of Chemistry and Physics, 37th edition, 1956, pp. 392-393). It concerns more particularly a process for hydrovisbreaking heavy petroleum fractions in order to convert them into lighter fractions.
Numerous processes for visbreaking or hydrovisbreaking hydrocarbon charges have been described in prior art and it is well-known that the conversion, which is carried out at a high temperature, depends on the operating conditions. However, when the operating conditions are too severe (high temperature and long residence time), unstable products form and there is also a risk of coke forming.
A means which is well-known by the man skilled in the art for compensating for this disadvantage consists in continuously injecting into the charge to be treated a metal or a metal compound having in the thermal treatment conditions a hydrogenizing activity (EP A 181,253, U.S. Pat. No. 4,655,905). The metal which is most often used to do this is molybdenum, which shows a hydrogenizing activity in the presence of hydrogen sulfide (H.sub.2 S).
Besides, it is also known by the person skilled in the art that it is advantageous to utilize, in the processes for visbreaking and/or hydrovisbreaking hydrocarbon charges, a catalyst in the form of a sulfide. As a matter of fact, said form shows a catalytic activity and a stability which are higher than those of the other forms which can be used, especially those of oxides.
It is also known that, apart from the quality of the catalytic precursor which is used, it is advisable to obtain catalysts that are well scattered in the charge to be treated.